1. Field of the Invention
This invention relates to an optical transmitting module and a method for controlling an output wavelength of the optical transmitting module.
2. Related Prior Art
In a Wavelength Division Multiplex (hereinafter denoted as WDM) communication system, various technique have been well known to maintain an output wavelength of a light source such as a semiconductor laser diode. One example of such techniques is to use a thermoelectric cooler. A temperature of the laser diode disposed on the thermoelectric cooler with a sensor for monitoring a temperature of the laser diode, and the laser diode is so controlled via the thermoelectric cooler that the temperature is kept constant based on the result of the sensing. This technique utilizes a characteristic that the output wavelength of the laser diode has temperature dependence.
In the conventional optical source using the laser diode for the WDM communication system, the temperature of the laser diode must be set to be within a predetermined range at a first step of the operation to prevent the laser diode from oscillating at an optional wavelength. Next, a bias current and a modulation current are provided to the laser diode. In such sequential steps, the temperature of the laser diode may rise due to self-heating by currents provided thereto, which shifts the output wavelength out of the predetermined range. Getting out of the range in the output wavelength, the currents provided to the laser diode are ceased, which restores the temperature of the laser diode. Afterward, turning on and shutting down the bias current are iterated.